In recent years, with the rapid development of the Internet technologies and the biometric identification technologies, some sophisticated fingerprint identification products have come into use rapidly in daily work and life. Currently, the fingerprint capture apparatus has evolved from flat capture to scan capture, which only requires the users sweep their finger balls on the sensor to get their fingerprint images. The cost of a scan capture chip is far less than that of a touch capture chip or an optical sensor for its compactness. And its dynamic and static power consumption is very low. Presently, this kind of fingerprint capture apparatus is applied broadly. Its capture principle is: the finger sweeps towards a specific direction, and the sensor captures many fingerprint image slices (frames) at the same time, then it figures out a full fingerprint image by mosaicing the slices with a fixed mosaicing algorithm. The slices are mosaiced in terms of gray scales, because the gray scale values of some pixels in two sequential frames are identical or similar. As the sweep direction is defaulted, it is not considered during mosaicing. However, if the sweep direction is reverse, the resulting image will be incorrect according to the original algorithm and cannot be further used to authenticate a user. Hence it is so inconvenient that the users must determine the sweep direction before they use a fingerprint capture apparatus.